The present invention relates to an optical addressing device used for a display apparatus which utilizes an electrooptic material, and a display apparatus using such an optical addressing device. More specifically, the present invention relates to an optical addressing device suitably used for a liquid crystal display apparatus, and a liquid crystal display apparatus using such an optical addressing device.
Liquid crystal display apparatuses are classified based on the driving method thereof into types of an electrical addressing method, a thermal addressing method, and an optical addressing method. Among these types, presently, a passive matrix (PM) type and an active matrix (AM) type of the electrical addressing method are most frequently used as direct-view display apparatuses.
In recent years, needs for a larger size and a higher precision of a display apparatus has increased. Conventional types of liquid crystal display apparatuses however have not satisfactorily responded to these needs. In reality, the largest size of 20 inches diagonally is the limit for products commercially available. Even for trial manufacture, the size is only about 30 inches diagonally. In particular, the PM type has a problem that the contrast is lowered due to crosstalk as the number of pixels increases. The AM type also has a problem that it is difficult to form a number of switching elements (especially, thin film transistors (TFTs)) without occurrence of defects.
A plasma addressed liquid crystal (PALC) display apparatus was developed in 1990 by T. Buzak and his colleagues of Tektronix Inc., U.S. as an AM type liquid crystal display apparatus which does not use semiconductor switching elements such as TFTs (see U.S. Pat. No. 4,896,149 and the corresponding Japanese Laid-Open Publication No. 1-217396, for example). The sectional structure of such a PALC apparatus is diagrammatically shown in FIG. 1.
A PALC display apparatus 100 has a layered structure consisting of a liquid crystal cell and a plasma cell. A liquid crystal layer 103 is sandwiched by a substrate 101 and a dielectric separator 104 and driven by a potential difference between signal electrodes (column electrodes) 102 and the dielectric separator 104. The plasma cell has a plurality of plasma discharge channels 105 formed by dividing a space between a substrate 109 and the dielectric separator 104 with a plurality of rib walls 106. Each plasma discharge channel 105 encloses ionizable gas therein so as to allow plasma to be generated by applying a discharge pulse voltage between a cathode 107 and an anode 108. The plurality of plasma discharge channels 105 extend in the direction perpendicular to the length of the signal electrodes (column electrodes) 102, and the cathodes 107 and the anodes 108 serve as scanning electrodes (row electrodes) 110, thus to effect line-sequential scanning.
In the PALC display apparatus described above, the size can be increased comparatively easily compared with a TFT-incorporated liquid crystal display apparatus. However, the PALC display apparatus has problems as follows. The dielectric separator 104 of the PALC display apparatus 100 is made of a glass thin plate, which is not only expensive but also difficult in handling. In fact, handling of such a glass thin plate becomes more difficult as the size of the display apparatus is larger, increasing the probability of fracture during fabrication of the display apparatus.
The surface of the glass thin plate on the plasma cell side serves as a pseudo-electrode during the driving of the PALC display apparatus. The thickness of the glass thin plate is about 50 to 100 microns, which is larger by ten times or more than that of a general nematic liquid crystal layer, i.e., 3 to 6 microns. In order to drive the PALC display apparatus, therefore, it is required to apply a voltage higher by ten times or more than a voltage with which the liquid crystal layer can be effectively driven. This causes problems such as increasing the burden on a drive circuit and increasing power consumption accompanied by heat generation.
Moreover, since the glass thin plate is fragile in strength, it is very difficult to form an electrode thereon. This is the reason why the electrodes for plasma discharge are formed in parallel with the plane of the substrate as shown in FIG. 1. This construction is not desirable since it reduces the aperture ratio of the display apparatus and thus lowers display quality.